Cohort trends in intrinsic capacity in Europe: a population-based longitudinal study

BACKGROUND: Intrinsic capacity is a comprehensive measure of physical and mental capacities central to the WHO healthy ageing framework. Studies from England and China suggest that trajectories in intrinsic capacity are improving in more recently born older adults. However, whether similar improvements are occurring in other countries, in adults younger than 60 years, or across socioeconomic groups remains unknown. METHODS: We analysed seven waves (waves 1-2, 4-6, and 8-9) of The Survey of Health, Ageing and Retirement in Europe (SHARE) between 2004 and 2022, including 80 105 adults aged 50 years or older in Austria, Belgium, Denmark, France, Germany, Italy, the Netherlands, Spain, Sweden, and Switzerland. Intrinsic capacity was derived using confirmatory factor analysis across five subdomains (cognitive capacity, psychological capacity, sensory capacity, locomotor capacity, and vitality). Multilevel growth-curve models estimated associations of birth year with intrinsic capacity at first interview and within-person change over follow-up and variation by country, sex, and socioeconomic status (categorised as low, middle-low, middle-high, and high). We present model-based predictions for specific birth years (1920, 1930, 1940, 1950, and 1960), referred to here as birth cohorts. FINDINGS: The analytical sample of 80 105 respondents contributed 222 761 person-waves across the seven waves of SHARE. Across analytical person-waves, the mean age was 67·7 years (SD 10·3) and 43 289 (54·0%) of participants were women. More recently born participants had higher intrinsic capacity at study entry (birth year coefficient 0·797 [95% CI 0·780 to 0·815], p<0·0001) and slower 10-year rates of decline (linear change × birth year 0·426 [0·372 to 0·480], p<0·0001) than participants born earlier, although these gains in intrinsic capacity at study entry became progressively smaller (birth year squared -0·092 [-0·096 to -0·089], p<0·0001) and the slowing rate of decline weakened (linear change × birth year squared -0·047 [-0·059 to -0·036], p<0·0001) in more recently born participants. Similar trends were observed for each subdomain. Countries with lower intrinsic capacity levels in the 1920 birth cohort, such as Italy, showed larger gains in intrinsic capacity at study entry than countries with higher initial intrinsic capacity, such as Switzerland (eg, from the 1920 to the 1960 birth year cohorts: Italy, intrinsic capacity at study entry -1·880 [95% CI -1·953 to -1·808], p<0·0001, to 0·283 [0·246 to 0·319], p<0·0001; Switzerland, -0·705 [-0·775 to -0·636], p<0·0001, to 0·576 [0·541 to 0·611], p<0·0001) but smaller improvements in rates of decline (from the 1920 to the 1960 cohort: Italy, annual rate of decline in intrinsic capacity over 10 years -0·092 [95% CI -0·104 to -0·080], p<0·0001, to -0·011 [-0·017 to -0·006], p<0·0001; Switzerland, -0·121 [-0·132 to -0·111], p<0·0001, to -0·009 [-0·014 to -0·004], p=0·00040). Intrinsic capacity at study entry increased among more recently born participants of both the sexes, with women showing larger gains in intrinsic capacity than men (birth year coefficient: women 0·813 [0·789 to 0·837], p<0·0001; men 0·735 [0·708 to 0·762], p<0·0001), resulting in progressive narrowing of the sex-based difference in intrinsic capacity at study entry. Gains in intrinsic capacity at study entry across birth years were larger in higher socioeconomic status groups (birth year coefficient differences vs low socioeconomic status: middle-low 0·053 [95% CI 0·010 to 0·095], p=0·015; middle-high 0·100 [0·053 to 0·148], p<0·0001; and high 0·081 [0·031 to 0·131], p=0·0015), resulting in a widening of socioeconomic status differences across successive birth cohorts. INTERPRETATION: More recently born Europeans aged 50 years and older are in better health and show slower declines in intrinsic capacity compared with previous generations. However, these positive trends are unequally distributed and could be reaching a ceiling. Policy makers cannot assume that these trends will continue. The improving rates of decline in some countries underscore the value of continued investment in health care for older adults. FUNDING: Australian Research Council Centre of Excellence in Population Ageing Research and Velux Stiftung.